Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

588
FXUS63 KLOT 240219
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
919 PM CDT Sat May 23 2026

.KEY MESSAGES...

- A few showers/isolated storms possible this evening. Much
  higher coverage expected early Sunday morning particularly
  along and east of I-55. Threat for locally heavy rainfall and
  perhaps some minor hydrologic issues in spots.

- Above normal temperatures are expected through early next
  week, though cooler conditions will occur near Lake Michigan
  each day.

&&

.UPDATE...
Issued at 919 PM CDT Sat May 23 2026

While some spotty showers will be possible this evening west of
the Fox Valley and also near a remnant lake breeze boundary
south of the Kankakee River, precipitation coverage looks
relatively sparse into the early overnight.

The main focus remains on the very late overnight period through
Sunday morning as a fairly energetic shortwave trough swings
eastward across the region. Guidance depicts gradually-
increasing upper divergence occurring around daybreak as two
(currently distinct) jet cores intensify and merge to some
degree with a commensurate increase in jet coupling taking
place. As this enhanced forcing encounters a ribbon of higher
PWATs (near 1.5"+ or 175 percent of normal) along a northeast to
southwest oriented moist axis, the expectation is for rain and
embedded thunderstorm coverage to increase fairly rapidly around
or just prior to daybreak. While instability is not going to be
substantial, tall/skinny CAPE profiles, seasonally deep warm
cloud depths, and cloud bearing winds largely paralleling the
initiating/forcing mechanisms suggest the potential for low echo
centroid type showers/storms with possibly deceptively high
rain rates and a localized training potential.

Additionally, the trend in guidance over the last 12 hours has
been decidedly upwards on the coverage and intensity of
convection through Sunday morning. Have commensurately boosted
PoPs to categoricals along and east of about I-55 Sunday
morning and will start to message the potential for isolated heavy
rainfall a bit more. Main time window is about 5 AM through 11
AM, with activity clearing our forecast area by early afternoon.

Carlaw

&&

.DISCUSSION...
Issued at 222 PM CDT Sat May 23 2026

An upper-level low over southern Manitoba will shift NNE
through tonight as a trough axis extending from the Arrowhead of
Minnesota to the Missouri River Valley drifts eastward.
Meanwhile, an ongoing occlusion of the associated low-level warm
sector is ongoing across eastern Iowa into southwest Wisconsin.

As low-level moisture increases via advection across western
Illinois (evident in the low 60s dew points and growing cumulus
early this afternoon), a scattered to broken axis of showers
with some embedded thunderstorms is expected to develop later
this afternoon over eastern Iowa and drift eastward across
eastern Illinois into this evening. Coverage of thunderstorms
remains questionable as modest mid-level warming should inhibit
deeper surface-based convection through sunset. Additionally,
weak flow of under 25 knots throughout the potential convective
layer would yield short-lived, slow-moving cells. That said,
decent low-level CAPE below the mid-level warming indicates
showers could produce locally heavy rain even in the absence of
thunder through this evening. Expectation is for the highest
chances to reside around and west of I-39 very late this
afternoon into mid-evening before shower and storm chances wane
with eastward extent late this evening into the early overnight
hours.

Continued low-level moisture advection ahead of the slow-moving
front tonight will then interact with a trio of forcing
mechanisms to increase shower coverage generally around and east
of I-55 late tonight and especially from sunrise to mid-morning
Sunday. Coverage may increase quickly as loosely coupled upper
jet streaks align with a secondary mid-level trough axis and
mid-level convectively enhanced wave currently emanating from
Oklahoma. Thunder chances again appear relatively low, but with
PWATs increasing to over 1.5 inches and the bulk of CAPE
supportive of low-centroid cells, efficient precip and swaths of
heavy rainfall appear likely. Also cannot rule out brief
funnels under any growing convection over the far southeast CWA
mid-morning as surface-based instability increases, though the
best chance appears over southern IL/IN closer to more favored
surface vorticity.

High pressure will then bring quieter conditions to the area
late Sunday through Memorial Day and possibly through Tuesday.
An attempt at Rex blocking is becoming more evident in guidance
mid to late week as ridging over the central and northern Great
Plains is undercut by a southwestern trough cutting off over
Texas and the Lower Mississippi Valley. Expansive Hudson Bay
high pressure Tuesday and Wednesday will drift southward across
the Great Lakes region late in the week, which should stave off
higher precip chances during this period. Between these windows
above, a backdoor front associated with the approaching wave may
bring a period of showers and some storms to the area Wednesday
before precip clears south by Thursday.

Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 636 PM CDT Sat May 23 2026

Forecast concerns include...

Ifr/lifr cigs/vis near Lake Michigan this evening.
Chance of thunderstorms around daybreak Sunday morning.
Mvfr, possible ifr, cigs early Sunday morning.
East wind shift with a lake breeze Sunday afternoon.

Fog and low clouds over far southwest Lake Michigan continue to
slowly move inland east of MDW and across GYY. This fog has been
slowly dissipating from north to south as well as over parts of
the lake. If these trends continue, the fog and low clouds may
dissipate over the next few hours but confidence is low and
trends will need to be monitored.

Isolated showers will be possible across parts of north central
IL this evening, including along the lake breeze as it moves
west, away from the Chicago terminals. Currently only expecting
a low chance of showers at RFD this evening. These showers may
slowly dissipate after sunset with a brief lull around midnight
and then additional showers are expected to develop overnight
and as an upper trough swings across the area in the predawn
hours, showers are expected to increase in coverage with at
least isolated thunderstorms possible. Some of the most recent
guidance would suggest a broken line of thunderstorms possibly
developing right over the Chicago terminals around daybreak
Sunday morning. Only medium confidence from this distance and
opted to include tempo thunder mention for this potential.
Showers will end during the mid morning hours and then dry
weather is expected for the rest of the period.

Cigs overnight into Sunday morning will likely be dependent on
precipitation coverage with mvfr cigs expected along with the
possibility for ifr cigs for at least a few hours.

Easterly winds around 10kt can be expected with the current lake
breeze as it continues moving west until it dissipates later
this evening. Easterly winds will become light and variable
overnight, then shift to the north/northwest Sunday morning as a
cold front moves across the area. Winds will shift easterly at
the Chicago terminals Sunday afternoon as a lake breeze moves
inland. Timing will likely needed some adjusting with later
forecasts. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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